#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
int main(void) {
	float a, b;
	float sub,ji;
	printf("input two numbers:");
	while (scanf("%f %f", &a, &b) == 2) {
		sub = a - b;
		ji = a * b;
		printf("%f\n", sub / ji);
		printf("input two numbers:");
		scanf("%f %f", &a, &b);
	}
	return 0;
}